Large variations in tuner settings from one end of 80M to the other end
is
normal. This is about typical of all tuners as the ratio of bandwidth to
frequency is greater on the lower frequency bands than on higher
bands/frequencies. I really haven't found a band or frequency or
reasonable
antenna below 30 MHz that the 238 tuner would not handle. {I've not tried
to
load a coat hanger. hi hi}
I do have a chart based on settings for all bands and several settings
vs.
frequency for each band, and for two different antennas. This makes for
quick tune-up when changing antennas or bands. I'll be glad to share
that
but it most likely would apply only to my antenna configurations, those
being a 1/2 wave for 160M fed with balanced line and a 1/2 wave for 75M
fed
with coax.
I do not suggest using a 4:1 balun for your configuration but a 1:1
current
balun. These are typically less lossy as you are not matching the feed
line
Z but the antenna load Z which is likely closer to 35 to 100 ohms or
less.
If you have an Antenna Analyzer measure the Z at the balun coax terminal.
You'll likely find that it is 10 to 25 ohms. This being the case then a
1:1
balun would be more nearly correct as the load with that configuration
would
be 40 to 75 ohms. Again, a better match for your coax between the balun
and
the tuner.
For whatever reason, using balanced line of some 400 to 600 ohms, hams
typically believe they should match the feedline Z. In actuality the
feedline is more correctly reflecting the antenna feed impedance. And is
some cases, acting like a transmission line transformer.
Here is a case where a 4:1 balun is accurately used. The old fashion
folded
dipole made of twin lead. The feed Z of a 1/2 wave folded dipole where
the
top and bottom conductors are of equal size is nominally 300 ohms when
greater than 1/4 wave above ground. Add an electrical 1/2 wave of
feedline
and one has an antenna with a feed impedance at the transmitter of about
300
ohms. Use a 4:1 balun and the transmitter feed is 75 ohms showing a SWR
of
1.5:1 . Drop the antenna down to less than 1/4 wave and the feed Z will
drop toward 200 ohms which then with a 4:1 balun the feed point for the
transmitter is now approaching 50 ohms.
73
Bob, K4TAX
----- Original Message -----
From: "Denton" <denton@oregontrail.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, April 11, 2008 12:28 AM
Subject: [TenTec] Ten Tec 238A settings?
I have a horizital loop up about 30' that has about 240' of wire in
roughly
a trapazoid shape....have found that by using a certain length of 600
ohm
feeders with a 4 to 1 balun, I have swr below 3.5 to 1 or below on all
bands
from 80 thru 10 meters, as measured at the balun's input...with the
exception of 17 and 60 meters. I am also using about 20 ft of good
quality
coax to the shack with a TT 238A tuner to take care of the minor swr on
the
system.
I notice that on 75 and 80 meters there is a large variation in tuner
settings from one end of the band to the other....is this typical of TT
tuners and L networks in general?
It appears to be a decent antenna system....if I can hear them, can work
them.
I have also verified the antenna's effiectiveness by also using it with
a
link coupled transmatch...by extending the 600 ohm feeders and running a
short stubb of 400 ohm line to the shack.
TT's L network gives me a much broader matching range, otherwise would
just
use the balanced transmatch.
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec